1. Field of the Invention
The present invention relates to a multi-band antenna, and more particularly, to a multi-band antenna and design method thereof using a Koch fractal antenna technology.
2. Description of the Related Art
Since the wireless communication technology of using electromagnetic wave to transmit signals has the effect of remote device transmission without cable connection, and further has the mobility advantage, therefore the technology is widely applied to various products, such as mobile phones, notebook computers, intellectual home appliance with wireless communication features. Because these devices use electromagnetic wave to transmit signals, the antenna used to receive electromagnetic wave also becomes a necessity in the application of the wireless communication technology.
FIG. 1 shows a comparison between a conventional Koch fractal antenna and a monopole antenna. Referring to FIG. 1, the conventional monopole antenna 101 is stretched outwards from its center portion for reducing the antenna size, so that an equilateral triangle is formed at the center of the original monopole antenna 101, occupied one-third portion of the monopole antenna 101. As shown in FIG. 1, the antenna 120 is a result of stretching the monopole antenna 101 from its center. In the FIG. 1, the antenna 123 is the equilateral triangle mentioned above, in which the length sum of the triangle sides is exactly one-third of the whole length of the original monopole antenna 101.
In this method, each side of the antenna 120 can be further stretched, to form the antenna 130 as shown in FIG. 1, wherein the side length of the equilateral triangle 133 formed by stretching the antenna 130 is one-third of each side of the original antenna 120. Thus, the shape of the antenna 140 can be formed by repeating the above steps. The antenna formed by the above method is a so-called Koch fractal antenna. The Koch fractal antennas of different arrangement can be designed by stretching the antenna repeatedly for different times.
After the original monopole antenna is stretched for different times, different operation wave lengths can be obtained. Therefore, the area occupied by the monopole antenna can be reduced by stretching the monopole antenna for different times, and also the required operation frequency can be achieved. Thus, the antenna can be minimized and implemented to fit different devices. However, such Koch fractal antenna design only enables the antenna to work in a single band, and cannot transmit and receive multi-band signals simultaneously.
FIG. 2 shows a conventional inverted-F dual-band antenna. In FIG. 2, the conventional inverted-F dual-band antenna comprises a radiation element 301, a grounding element 303, a conductive pin 305 and a signal wire 307. The radiation element 301 is a straight wire made of electrically conductive material to receive and transit signals with two frequencies f1 and f2. The length of the radiation element 301 is determined by the two different frequencies f1 and f2, and the radiation element 301 can be further divided into a first section 311 resonating at the first frequency f1, and a second section 309 resonating at the second frequency f2. The first frequency f1 is different from the second frequency f2. The length l1 of the first section 311 is approximately one-fourth of the wavelength λ1 of the first frequency f1, while the length l2 of the second section 309 is approximately one-fourth of the wavelength λ2 of the second frequency f2.
The grounding element 303 is a conductive plate underneath and separated from the radiation element 301 with a gap. The conductive pin 305 is connected to the radiation element 301 and grounding element 303 to form an N-shape structure. One end of the signal wire 307 is connected to the conductive pin 305 to receive or transmit electromagnetic waves. Even though this inverted-F dual-band antenna can be adapted in receiving and transmitting signals with two different operation frequencies, the radiation element 301 therein cannot be further shrunk or deformed. Therefore, inverted-F dual-band antenna cannot fit into small devices. Accordingly, such design is relatively inconvenient.